Field of the Invention
The present invention relates to an imprint apparatus for molding an imprint material on a substrate by using a mold having patterns formed on it.
Description of the Related Art
An imprint technique which molds an imprint material on a substrate by using a mold having patterns formed on it is attracting attention as a technique of producing a microstructure device. In this imprint technique, a mold having projection-and-recess patterns is used as an original, and the patterns are transferred onto an imprint material on a substrate such as a wafer or glass substrate.
In this process, a separation force of, for example, 100 to 500 N is necessary to separate, from the mold, the imprint material having cured as it has entered gaps between the patterns. Accordingly, many defects may occur due to pattern transfer.
For example, FIG. 13 schematically shows the state of a substrate 1 and mold 2 during separation. Referring to FIG. 13, an imprint material 3 has cured as it has entered between patterns 22 formed on the surface of the mold 2. When lifting up the mold 2 in order to separate it, it is necessary to apply a force of separating, from the patterns 22, the whole imprint material 3 having cured as it has entered between the patterns 22. In this case, after a thin portion of the mold 2 deforms, stress concentration generally occurs in the peripheral portion of the patterns 22, and separation starts from this portion and momentarily spreads over the entire surface. In this state, the patterns 22 are strained in the portion where the stress concentration has occurred, and the strain distribution spreads as the separated portion spreads. As described previously, a force of 100 to 500 N or more is necessary to separate the mold 2 from the imprint material 3. Since this force is momentarily released in the separated portion, a defect such as chipping or deformation sometimes occurs during separation on the patterns 22 of the mold 2 or on the patterns transferred to the cured imprint material 3. FIG. 14 shows a state in which the strain thus produced remains on the substrate 1 immediately after separation. At address A1 of a semiconductor element having undergone separation, an original chip shape 34a deforms into a strained shape 35a. In addition, this shape change exerts influence on addresses adjacent to address A1. For example, at address A2 of the semiconductor element, an original chip shape 34b deforms into a strained shape 35b. Likewise, at address A9, an original chip shape 34c deforms into a strained shape 35c. 
In Japanese Patent Laid-Open No. 2012-234913, to prevent the accumulation of this strain on the substrate 1, chucking by a substrate holding mechanism is temporarily released after separation, thereby releasing the residual stress on the substrate 1. Also, in Japanese Patent Laid-Open No. 2010-098310, as shown in FIG. 15, an electrostatic attracting portion of a substrate holder is divided into a plurality of attracting blocks 36, and a controller 11 can partially switch ON/OFF of attracting forces. This makes it possible to partially release attractive fixing of the substrate 1 after separation, and partially release the residual stress.
Unfortunately, the conventional imprint apparatuses do not suppress the occurrence of a strain or defect itself. Therefore, it is possible to release the chucking force of the substrate holder by partially turning off the chucking force after separation is complete, but it is not possible to prevent a strain or defect of patterns which occurs during separation. Also, the division of the chucking regions is set in accordance with the substrate size. If the substrate size is changed, therefore, the substrate holder must be replaced, so the productivity decreases.
Furthermore, if the force (to be referred to as a “separation force” hereinafter) required for separation exceeds 200 N, this force exceeds the force with which the substrate holder chucks the substrate, and the whole substrate is sometimes separated from the substrate holder. This makes it impossible to separate the cured imprint material from the mold. Alternatively, a portion of the substrate is sometimes momentarily floated from the substrate holder and chucked again. In this floated portion, a flaw or damage occurs due to friction between the lower surface of the substrate and the substrate holder.